Retirement Plans - Schedule of Actuarial Assumptions Used in Determination of Net Periodic Pension Cost (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Weighted average discount rate	3.17%	4.16%	4.19%
Rates of increase in compensation levels	3.50%	3.50%	3.50%
Expected long-term rate of return on assets	7.25%	7.25%	7.25%